Differential Host Use of Helianthus by Two mtDNA Lineages of Strauzia longipennis

Host race formation is believed to be an important step in the formation of new species. Several varieties of Strauzia longipennis may exhibit differential host use, either by being host-taxon specific or by being host-tissue specific. Data already collected at Cornell College revealed two distinct populations of S. longipennis, which differ both morphologically and genetically. One population corresponds to descriptions of S. longipennis, and the other corresponds to descriptions of S. longipennis var. vittigera. I collected larvae from the stems of host plants in late summer, and measured the diameters of stems at the point of infestation. The population of larvae formed a bimodal distribution with respect to stem diameter. Once the identities of these larvae are determined genetically, I predict that S. longipennis and var. vittigera will show different patterns of host use: one may infest narrow stems and the other may infest wider stems.